This invention relates to cardiac pacemakers and, more particularly, to the orientation and shape of the electrodes of a pacemaker catheter.
Cardiac pacemakers have been extensively used in patients with poorly functioning heart pacing mechanisms due to breakdown in the cardiac electrophysiological system. The pacemakers rectify malfunctioning systems by stimulating the heart with electrical impulses and thus controlling the heart beat rate.
In normal functioning cardiovascular systems, electrical signals are produced by the sino-atrial (S-A) node. The S-A node controls the heart beat by stimulating the heart muscles through electrical signals of sufficient magnitude and accurate sequential timing. The electrical signals are conducted from the S-A node to the right and left atria, and are also transmitted from the atria through the AV node to the right and left ventricles, which respond to the depolarizing wave and produce contraction of the heart muscle. Malfunction in the AV node conduction system between atrium and ventricle sometimes results in failure or block of the transmitted signal. Simple cardiac pacemakers supply a stimulus signal to the ventricle and thus cause the heart to beat at a fixed rate.
Various other cardiac pacemaker system types have been used in the past, and the most widely used of these are discussed in U.S. Pat. No. 4,365,639 to Goldreyer. One such system uses two catheters, one positioned in the ventricle and the other within the atrium, respectively. The stimulating electrodes disposed on each of the catheters were operated at a set rate, and with a time lag between the stimulating pulses. Several drawbacks to such a sequential pacing system were discovered, among them that two catheters were necessary for implantation in the heart and that cardiac output was only augmented by about 5 to 15% with fixed rate pacing. Also, two catheters were found to be overly bulky and, furthermore, because the system only operated at a rate fixed by the pacemaker, the heart could not compensate by increasing the heart beat rate if the patient experienced increased activity.
Other systems relied on a sensing mechanism where the cardiac pacemaker had both stimulating and sensing electrodes, or alternatively, one of the electrodes could act both as a sensor and as a stimulator. For these types of systems, the sensor would be set to sense a certain type of distinctive electrical wave pattern, known as a P-wave associated with atrial depolarization, which is the signal sent to the heart muscle in the ventricle via the AV node which causes the ventricle to contract. If a distinctive P-wave is sensed after a predetermined time interval from the last P-wave, the stimulating electrodes would then supply a pulse of energy of sufficient magnitude to stimulate the heart muscle into contraction at the proper time in the heart beat cycle.
With these types of systems, however, it becomes increasingly important that the electrical signal be detected accurately and consistently. Several of the aforementioned systems, as well as others, have emphasized the basic subject of endocavitary detection of cardiac signatures of the electrical signals associated with cardiac depolarization. Optimization of detection of signals in the atrial chamber of the heart is of particular importance because of the weak signals obtainable from the traveling wave front along the atrial myocardial wall during atrial depolarization.
Aforementioned U.S. Pat. No. 4,365,639 discloses a method to detect signals in the heart by the use of electrodes normal (orthogonal) to the plane of the depolarizing wave in the atrial cardiac tissue. However, the configuration of the electrodes on the catheter, and especially their shape and orientation in relation to each other, failed to take advantage of characteristics peculiar to the electrical signatures of cardiac waves in order to more accurately and consistently detect the signals indicative of a traveling wave front, such as a P-wave. Accordingly, it is an object of the present invention to improve the detection of physiologic electrical signals by optimizing the electrode configuration over that known to the prior art.
It is another object of the present invention to increase the sensitivity of a P-wave detection mechanism for providing a signal indicative of the passing of a P-wave to a cardiac pacer.
It is yet another object of the present invention to provide a catheter for a cardiac pacemaker system which takes into account various factors such as the extracellular potential field dimensions, the propagation direction of the field, anomalies in the conducting muscle fiber associated with age, and the practical impedance level of the electrodes as it relates to the electrode surface area, as well as to other factors.
It is still another object of the present invention to provide a new and improved electrode system which will provide for varying the heart rate in response to the body demand while at the same time utilizing only a single catheter inserted through a vein, without necessitating open heart surgery. A particular object of the invention is to provide an improved sensing electrode arrangement for detection of P-wave signals for controlling the timing of ventricular stimulation.
It is also an object of the present invention to provide a catheter for sensing and for stimulation in the form of a single non-diverging filament having two sensing electrodes mounted on the catheter with optimal placement, shape, size and orientation of the catheter electrodes.
It is a further object of this invention to provide for electrode sizes that are small as practical relative to the dimensions of the width of the traveling wave front and small relative to the dimensions of the field gradient normal to the wall of depolarizing muscle.
It is yet another object and a significant advantage of the present invention to optimize the parameters of the catheter electrodes in a pacemaker system so as to increase the effectiveness of the cardiac pacemaker system.
It is also an advantage of the present invention to adjust the placement, shape and orientation of the electrodes on a catheter of a cardiac pacemaker system so as to tune the electrode parameters to the peak negative to peak positive distance in the sensed traveling wave front of the depolarizing wave indicative of the physiologic signals creating a heart beat.
It is a further advantage and a unique feature of the present invention to allow the adjustment of the catheter electrode parameters so as to be suitable for the individuals having a variety of ages, heart sizes and heart conditions.
It is another feature of the present invention to provide optimal size, placement and orientation of the atrial electrode array so as to fully take advantage of the characteristics of the P-wave to improve sensing effectiveness.
In accordance with these and other objects, features and advantages of the present invention, there is provided a catheter for use in a cardiac pacemaker system with electrode pair arrangements limited to two electrodes operating together in a direct or differential bipolar configuration for sensing cardiac depolarization in the blood pool and not requiring contact with cardiac tissue.
The electrodes are so configured on the catheter relative to the cardiac depolarization wavefront direction to prevent signal cancellation or excess signal mitigation when the signals sensed from each electrode of the pair are electronically subtracted.
The electrode pair is configured so that the electrodes are placed on opposite sides of the catheter body but displaced longitudinally equal to or greater than the length of the depolarization signal along the axis of the catheter and more or less parallel to the axis of depolarization to allow the combinational features of controlling the electrode dimensions in all three planes to minimize field averaging in all planes and to prevent signal cancellation as the depolarization wave passes each electrode.
The invention will be better understood and additional objects, features and advantages will become apparent from the following description of the preferred embodiments with particular reference to the drawing figures, wherein like referenced numerals indicate like elements.